1. Field of the Invention
The invention relates generally to inert gas distribution systems, such as those used on aircraft. More specifically, the invention relates to a system and method for monitoring and/or controlling an inert gas distribution system.
2. Description of Related Art
The energy requirements of most modern aircraft are supplied by combusting aviation gasoline, which is typically stored in fuel tanks within an aircraft's wings. Such fuel tanks also contain an explosive fuel/oxygen mixture in the area above the fuel, otherwise known as the ullage. Accordingly, many systems have been developed to reduce the danger of accidentally igniting this fuel/oxygen mixture.
One way of addressing such a danger is to replace the explosive fuel/oxygen mixture with a nonflammable inert gas, usually nitrogen. One method to accomplish this is the On-board Inert Gas Generating System (OBIGGS), which separates nitrogen from local, ambient air and replaces the fuel/air mixture in the ullage with this nitrogen. An example of such as OBIGGS is disclosed in co-pending U.S. patent application Ser. No. 10/308,971, now U.S. Pat. No. 6,729,359, which is incorporated herein in its entirety.
Military aircraft have used OBIGGS for many years to protect against fuel tank explosions caused by extreme aircraft operation and exposure to small arms fire. However, military aircraft are not the only aircraft that would benefit from OBIGGS. For example, investigations into the cause of recent air disasters have concluded that unknown sources may be responsible for fuel tank ignition and explosion. Subsequently, OBIGGS has been evaluated as a way to protect commercial aircraft against such fuel tank explosions caused by any ignition source.
Current systems that monitor the performance (health) or effectiveness of inert gas generating systems, monitor the oxygen concentration, flow and/or pressure of the Nitrogen Enriched Air (NEA) output from the inert gas generating system. Using this data, together with predictive analysis, the oxygen concentration of the space is determined. As this is done by using both performance data and analysis, the oxygen concentration in the space is inferred, rather than measured directly. This inferred oxygen concentration is often inaccurate or incorrect, thereby negating any value that the monitoring system may have.
Furthermore, current oxygen sensor technology is incompatible with hydrocarbons and, therefore, generally cannot be placed directly into a fuel tank. This is because current oxygen sensors operate at elevated temperatures, which presents a serious explosion risk within the fuel tank.
In light of the above, it would be highly desirable to provide a system and method for monitoring the performance of an inert gas distribution system that directly senses the gas within a space to be inerted, while using standard sensor technology.